Quick and Easy Rocket Stove Hot Water Heater

Ojaipermaculturevid
This design is incredibly simple! The wonderful thing about these water heaters is that they are just insulated water tanks with a chimney exhaust running straight up through them for the propane burner at the bottom. I just took off a tray at the bottom, removed the propane hardware and exposed the 6 inch diameter chimney which fit a stovepipe perfectly. I made a basic "j" shape with the scap stovepipe i found and put it up into the bottom if the chimney. It has a built in blow off valve so it doesnt explode. The water mass heats up in about twenty minutes and yes, it roars! No smoke just steam. Feedback?

it's clear that it works, which is great. nice work. there's plenty of room for improvement, though, so don't rest on your laurels.

I thought of something different: instead of running a water pipe through the stove itself, why not run it in the thermal mass of a rocket stove mass heater? This would be much safer, because it runs at thermal mass temperature, not stove temperature. You also have warm water long after your fire died out.

I would use a standard setup for a solar water preheater with electric boiler, but swap the solar tube panel for the thermal mass of my rocket stove. The controller goes on the water piping of the thermal mass in the living room instead of a solar tube panel on the roof. When the water in the electric boiler tank reaches the lower threshold temperature, the controller checks if the thermal mass of the stove is hot. If it's warmer than the temperature needed in the boiler, it starts a small pump and runs the tank water through the thermal mass in order to reach the higher threshold. You then use no electricity in your boiler, only some minimal amount to run the pump. If your thermal mass is too cold, it just works as a regular electric boiler. This is pretty much foolproof, as long as you don't run your water piping too close to the fume pipe in the thermal mass: you certainly don't want to reach boiling temperature. Just in case, I would fit an extra safety valve on the thermal mass circuit. You also have a working electric boiler for the days you are too lazy to start a fire.

I think I actually could use both solar heating and mass stove heating on the same electric boiler. 'Still checking the controller side of that to use standard systems...

Any thoughts about that setup?

I picture copper tubing coiled around the the duct not too far down stream from the manifold. Is that like what you had in mind?

I'm developing a physical computing class for the middle school where I work. It seems like this would be an interesting place to aim some adult lesson plans. I can imagine a combined workshop with participants learning the science of the RMH, building one, and embedding a sensor network to measure things like the content and temperature of the exhaust gas along the length of the duct. Then, once it's cured, someone could burn the thing for a long time and keep track of the internal conditions of the system. That would help to decide where to place the coil in the final design to make as sure as possible it will not be able to heat water beyond a safe temperature.

You could also embed temp sensors in the mass to help locate a different place to locate some kind of mass-to-water heat exchanger. That would be easy in a pebble style RMH - just dig up the sensors and burry the exchanger in the same place. With cob and the like you'd have to build a test bench before the final bench or design for partial demolition and repair

Since I'm kind of a geek I would also want to incorporate thermoelectric generation to run the controller and maybe even the pump - and charge this laptop when the pump isn't running, and maybe an LED lamp for when I'm up late reading Permies. The design would need to protect the unit(s) from excessive heat and make them easily accessible because I'd want to experiment with them.

I don't think this kind of high tech stuff turns up often on the forums so I hope it doesn't offend anyone's sensibilities. But this stuff has become so cheap and accessible, I've come to view them as an appropriate technology to apply in the development and refinement of low-tech. We use electrically powered vehicles and tools in our large-scale projects, why not an electrically powered (and cheap) nervous system in our smaller-scale projects?

Hi Jeff,
This company sells double combustion stoves that can be fitted with a water-heating module:
http://www.walltherm.ca/
They also have a solar panel module that integrates with their hot water tank and controller.
Their system can use both very hot water from a stove radiator, and mildly hot water from a solar panel. Therefore, it should be perfectly feasible to set up a similar system with a radiator embedded in the thermal mass of a rocket stove. They use a small circulation pump, which is cheap, needs little power, and allows great control of the radiator temp. This is standard hardware, so I feel quite confident about giving it a try.
There still is the question of how to locate the heat exchanger in the thermal mass. I am thinking of embedding a standard flat radiator straight into the thermal mass with a slanting angle, without getting too close to the fume pipe. The idea is to get a constant, comfortable temperature, instead of designing for a fast heat-up with boiling risks. I would definitely fit a safety valve on the system. Anyway, the whole set-up should be very much the same as for a solar panel, swapping the solar panel for a radiator put into the thermal mass.
Besides, if you choose floor heating, the design temperature is barely above you target room temperature, so you actually would rather avoid high temps. Instead, the huge thermal mass at mild temperature of the mass stove provides an ideal large buffer at constant temperature.

- In the 50s and 60s it was still possible to find retirement hotels in Mexico that had "Rapidos'' ether wood fired or coin operated propane/butane/ nat gas water heaters,
usually located in a communal bathroom, one or two per floor, you built a little wood fire in the ''Rapid0'', and the wood fire took the chill of of the 'bathroom'', and soon
you had hot water, In these old "pen/si`/on/ees`'' (wrong word or spelling ) there was a pecking order, and if the unit on your floor had a chimney fire, or too much of
the floor was rotted out, you were dependent on being allowed to use 'their shower/bathroom' and the pipes could be heard banging at 2 a.m.as showers were taken to
avoid disturbing the schedules of people whose Bathroom 'Rapidos' still worked !!

Basically I am saying, this is just a modern-day re-invention of technology going back to the 1930s at least ! Big AL !

i had the same idea, but thought the water in the tank would drive down combustion temps so there wouldn't be as complete a combustion--but if you are getting steam out that's wonderful


of course all the old water heaters i have use a 4" core, so that would take alot of tending a very small fire

How hot is the exhaust? is there any more heat to be reclaimed there?

Allen - some times, I feel a twinge of sadness when I think about how much of the work that folks do in Permaculture, Transition, relocalization, etc. is really just figuring out stuff that people probably used to regard as common knowledge. There's no value in dwelling on that, though .. and I'm happy that so many examples of advancing the craft are so readily at my fingertips. Amazing times!